1. Field of the Invention
The present invention relates to a tandem AC generator for a vehicle (or a tandem vehicle alternator in short) capable of supplying different output voltages such as a high voltage and a low voltage.
2. Description of the Related Art
There have been proposed various types of manners of fixing dual armatures in a tandem AC generator. In the tandem AC generator, dual armature-Lundel type field winding pairs are placed in series along the direction of a rotary shaft.
One of the related-art manners, Japanese patent laid open publication number JP S56-112866 has disclosed a manner of fixing in series a primary housing, a primary armature, an intermediate spacer and a secondary housing. In the manner, a secondary armature is fixed to a position different from the positions of fixing the primary housing, the primary armature, the intermediate spacer and the secondary housing. Such a related-art manner of fixing the armatures decreases the accuracy of core axis by accumulating the tolerance of each component forming the AC generator. This increases the difference of the axis core of dual stators along the direction of the diameter. Still further, this related-art manner has a drawback in that it is too easy to shift the Lundel type field windings because the primary and secondary housings supporting the Lundel type field windings are easily shifted in the direction of the diameter.
Another related art document, Japanese patent laid open publication JP H05-83906 has disclosed another fixing manner in which a single housing supports dual armatures and a through bolt does not fasten the armatures in the axis direction of a rotary shaft. Accordingly, this manner has a drawback of being difficult to fix the armatures in the axis direction surrounded by the housing.
In order to solve the drawback of the related art, Japanese patent laid open publication JP 2005-229748 (the same assignee with the present invention) has proposed an improved manner to place an intermediate housing between dual armatures, and to place the intermediate housing and dual armatures between a front housing and a rear housing and to fasten them by through bolts in the axis direction. (Hereinafter, this connection manner will be referred to as “a through-bolt fastening manner”). This manner prevents the decrease of accuracy of the axis core by the components forming the tandem AC generator.
However, because fixing the armature based on the through-bolt fastening manner described above uses the intermediate housing between the dual armatures in the tandem AC generator, the accuracy of axis core between the housing and the armatures is decreased, and this manner introduces the difficulty to tightly fasten the armatures toward the axis direction of the rotary shaft in the tandem AC generator. In addition, the related art manner has a drawback of increasing the outer diameter and the total weight of the tandem AC generator by the presence of the intermediate housing. When the intermediate housing of a thin thickness is used in order to eliminate the drawback described above, the entire strength and durability of the tandem AC generator is decreased.